Technical Field
The present invention relates to a technique for detecting a target by using a radar and a camera.
Related Art
For example, a collision avoidance system for a vehicle is required to accurately detect a target such as another vehicle or a pedestrian. In response to this, JP-A-2006-292475 discloses a configuration for detecting a target by using a radar and a camera. Specifically, according to the configuration disclosed in JP-A-2006-292475, a target is detected by a millimeter-wave radar and a stereo camera individually. If the position relation between the target detected by the millimeter-wave radar and the target detected by the stereo camera meets a criterion for judgment, it is determined that the targets are the same. When the distances from the millimeter-wave radar and the stereo camera to the target are longer, the criterion for judgment is changed so that the targets are easily determined to be the same.
Meanwhile, detection information of the radar is suited to measure distances because the distances can be measured based on radar waves reflected from the target. However, it is uncertain which position on the target the radar wave is reflected from. Hence, an error corresponding to the breadth (width) of the target (target width) is generated, which is relatively disadvantageous to measure the direction of the target.
Although image information from the camera has performance of measuring distances lower than that of detection information from the radar, the target can be identified based on an actually picked up image. Hence, the image information of the camera is suited to measure the target width and the direction.
Hence, the radar and the camera are used to detect the target. Thereby, the radar and the camera mutually complement measurements at which the radar and the camera are poor to improve accuracy in detecting the position of the target. In this case, a step is required first in which the identity between the targets is determined based on the detection information of the radar and the image information of the camera.
However, regarding the image information of the camera, when the road gradient of the position of the vehicle is different from the road gradient of the position of the target, or when the vertical direction of the camera varies due to a pitching of the vehicle even if the road gradients are the same, the point at infinity on the image is shifted from the actual point. Thereby, it can be considered that, for example, a measurement error of the target width is generated.
Hence, for example, as in the case of the configuration disclosed in JP-A-2006-292475, if the criterion for judgment is merely relaxed depending on the distance to the target, the difference between the road gradients and influence of the pitching of the vehicle are not reflected. Hence, accuracy in determination concerning the identity of the targets may be lowered.